Vulnerability in Mpdavis Python-Jose
CVE-2026-85394
python-jose through 3.5.0 fails to properly validate asymmetric keys in HMAC initialization, accepting DER-encoded public keys that lack PEM armor or SSH prefixes. Attackers holding the service's public key can forge HS256 tokens that pass verification when algorithms are not explicitly restricted. This is an incomplete fix for CVE-2024-33663.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 9.1 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N.
EPSS exploit prediction
EPSS: 0.002 (11.9th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 12th percentile — 11.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.002 · change: 0.000
Affected products
Weakness classification (CWE)
References
- github.com/advisories/GHSA-6c5p-j8vq-pqhj (related)
- github.com/mpdavis/python-jose (product)
- github.com/mpdavis/python-jose/blob/018b310ddb8b50dcfd09a0c152117835a21dd656/jo… (technical-description)
- github.com/mpdavis/python-jose/blob/018b310ddb8b50dcfd09a0c152117835a21dd656/jo… (technical-description)
- github.com/mpdavis/python-jose/issues/414 (issue-tracking)
- www.vulncheck.com/advisories/python-jose-through-3.5.0-algorithm-confusion-via-… (third-party-advisory)
Frequently asked questions
- What is CVE-2026-85394?
- CVE-2026-85394 is a critical-severity vulnerability in Mpdavis Python-Jose, classified under Improper Verification of Cryptographic Signature. CVSS score: 9.1/10. Published 2026-09-03.
- How severe is CVE-2026-85394?
- Critical severity. CVSS v3 base score is 9.1 out of 10.